Spiders make their webs from silk extruded by special organs known as spinneret glands. But spinnerets are located at the tip of a spider's abdomen, not its limbs. So is Peter Parker anatomically incorrect? Well... not exactly.
We had the pleasure of hanging out with the entomologist known online as Bug Girl this weekend, during which time she was cruel enough to remind us of a certain uncomfortable factoid about the friendly neighborhood web-slinger, namely the true nature of the sticky stuff he's slinging. Bug Girl explains on her blog:
Spider-man's spider webbing talent isn't what you think it is. Sure, male spiders do have special appendages on the front of their bodies — they are really noticeable "boxing gloves." They actually can be up to 20% of a male spider's body weight.
Those are not, however, what spiders shoot silk or webbing out of. These pedipalps have one function. SEX.
That white, sticky stuff Peter Parker is shooting out of his wrist? Um. Yeah.
Surprise! It's spider jizz! Much, much more on the horrible truth behind Spider-Man's anatomy, over at Bug Girl's Blog.